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Louis K. Hirsch, Parameswaran G. Sreekumar, Christine Spee, Ernesto Barron, Laurie Dustin, Stephen J. Ryan, David R. Hinton; TGF-Beta 2 is the Predominant TGF-Beta Isoform Secreted by RPE in Polarized and Non-Polarized Cultures. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1654.
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Retinal pigmented epithelium (RPE) secretes fibrogenic proteins, e.g. transforming growth factor beta 1 & 2 (TGF-β1 & -β2). While both isoforms may promote fibrogenesis, TGF-β2 has a stronger association with ocular pathology, such as in proliferative vitreoretinopathy (PVR). Since RPE cell polarity may be altered in PVR, we studied the effects of polarity on TGF-β isoform secretion.
(1) Human Fetal RPE culture: RPE from 4 donors were cultured under 3 conditions for comparison: subconfluent nonpolarized, confluent nonpolarized, and highly polarized monolayers. (2) Enzyme-linked immunosorbent assay (ELISA): TGF-β1 and TGF-β2 were measured in media from apical and basal compartments of polarized RPE transwell filters and from the single compartment of nonpolarized RPE petri dishes. (3) Transepithelial Resistance(TER): To confirm RPE differentiation, donors had TERs of >185 Ω•cm^2. (4) Normalization: Data normalized by total cell protein assays.
Comparing secreted concentrations of total TGF-β1 to -β2, -β2 was secreted in higher concentrations than -β1 in all 3 culture conditions, polarized (p<0.01), nonpolarized confluent (p<0.01), and nonpolarized subconfluent (p<0.01). Total TGF-β is the sum of both latent and endogenous active forms. RPE also secretes significantly more endogenous active -β2 during in nonpolarized confluent (p<0.001) and subconfluent cultures (p<0.001).
RPE secretes higher concentrations of TGF-β2 than -β1 in both polarized and non-polarized cell cultures. These data are consistent with previous reports that -β2 is the predominant ocular isoform. These data contribute to our understanding of the cytokine environment created by the RPE. Further investigation into these cytokines may lead to targeted molecular therapies for fibrogenic ocular diseases like PVR.
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